Devel::FastProf is a perl per-line profiler. What that means is
that it can tell you how much time is spent on every line of a perl
script (the standard Devel::DProf is a per-subroutine profiler).

The former Devel::SmallProf accomplishes the same task, but it is
much slower. Devel::FastProf is only 5 to 8 times slower than normal
execution.
